Compressing a hard drive is a double-edged sword. While compression can greatly increase the amount of space on a drive, it also slows it down, requiring your computer to decompress and re-compress any information it accesses. If a compressed C drive (the primary hard drive for your computer) is bogging down your PC, decompressing it could help speed things up. However, the process is time consuming, and it could take several hours. This method works on all versions of Microsoft Windows.
Click the "Start" button on the taskbar and open "My Computer" or "Computer" (varies depending on your version of Windows).
Right-click the "C" drive and select "Properties." This opens the Properties menu for the drive. If the Properties menu doesn't open to the General tab, switch to it.
Study the graph and numbers on the General tab. The drive's overall capacity, space available and space used are listed. A pie graph is also on the menu, depicting a visual of the space used on the drive. If more than half of your drive is already in use, you need to move or delete files from the drive to clear space. However, it's a good idea to backup a drive before decompression anyway; just to be safe.
Connect an external hard drive to your computer (its drivers will install automatically). If your external drive is larger than your PC's drive, you can backup your entire C drive to the external drive by clicking the Tools tab on the Properties menu and clicking the "Back up now..." button. If it's smaller, you need to decide which files to manually transfer to the external drive.
Browse your computer, deleting unnecessary files and moving others to the external drive (right-click the file, click "Send to" and select the external drive). Do this until more than half of your C drive is freed-up.
Return to the General tab on the Properties menu and un-check the box "Compress this drive to save disk space." Then click "Apply" and "OK." Your computer will now decompress the C drive. Follow any further instructions it gives you.
Backing up your entire C drive before decompression is the safest route to travel. This guarantees you won't lose any data if something goes wrong during the decompression.